The present invention relates to optical communication networks and, more particularly, to optical devices for routing multi-wavelength optical signals.
When multiple users share a transmission medium, some form of multiplexing is required to provide separable user sub-channels. There are many multiplexing techniques available that simultaneously transmit information signals within the available bandwidth, while still maintaining the quality and intelligibility that are required for a given application. Optical communication systems, for example, increasingly employ wavelength division multiplexing (WDM) techniques to transmit multiple information signals on the same fiber, and differentiate each user sub-channel by modulating it with a unique wavelength of invisible light. WDM techniques are being used to meet the increasing demands for increasing speed and bandwidth in optical transmission applications.
In optical communication networks, such as those employing WDM techniques, individual optical signals are often selectively routed to different destinations. Thus, a high capacity matrix or wavelength selective cross-connect (WSC) switch is often employed to selectively route signals through interconnected nodes in a communication network. Many wavelength selective cross-connect switches used in optical communication networks are either manual or electronic, requiring multiple optical-to-electrical and electrical-to-optical conversions. The speed and bandwidth advantages associated with transmitting information in optical form, however, makes an all-optical network the preferred solution for WDM-based optical networks. Moreover, all-optical network elements are needed to provide the flexibility for managing bandwidth at the optical layer (e.g., on a wavelength by wavelength basis).
One problem with the current design of wavelength selective cross-connect switches is that to service the WSC, both fiber optic lines must be broken. As the demand for optical bandwidth increases in WDM communication systems, it is desirable to increase the number of channels. The number of wavelength channels in commercial fiber optic line systems, for example, now typically exceeds one hundred channels. Unfortunately, an increase in the number of channels provides a corresponding increase in the size, cost and insertion loss of the optical devices in such WDM communication systems. More specifically, filters that can handle all the channels independently with wide, flat bands become very large and difficult to make with high yields, regardless of the technology. A need therefore exists for an improved wavelength selective cross-connect switch that permits serviceability without traffic interruption in an efficient manner. A further need exists for an improved wavelength selective cross-connect switch that uses a periodic filter design to tradeoff flexibility for greater device simplicity.
Generally, a wavelength-selective cross connect switch is disclosed that can selectively pass a multi-wavelength incoming signal received on a given incoming port to a corresponding output port in a bar state; or cross the received signal to an opposite output port in a cross state. The wavelength-selective cross connect is fabricated using only two wavelength blockers and a number of optical circulators.
Power splitters divide the power of each incoming signal in half and the half-power signals are applied to the two wavelength blockers surrounded by corresponding optical circulators. Each of the wavelength blockers control either the bar state or the cross state. The outputs of the two wavelength blockers are combined to produce an output signal at each of the output ports. Thus, the wavelength-selective cross connect can selectively pass or cross an incoming signal to an appropriate output port, as desired.
The disclosed wavelength-selective cross connects can be serviced without interrupting traffic. For instance, suppose one of the wavelength blockers needs to be replaced. The network can be configured so that all of the channels are in the bar state. Then the blocker can be removed without interrupting any traffic. Another main advantage of the present invention is that a device that requires only shutters, i.e., the wavelength blocker, is significantly easier to make than a device requiring switches, such as typical WSCs.
A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings.